In a skillet over medium heat, whisk the flour into the warm fat.  Cook, stirring constantly, until the flour just starts to brown and smells nutty.  Slowly whisk in the chicken broth and stir until smooth.  Add the undrained tomatoes.  Add salt and pepper to taste.  Cook until thickened - about 5 minutes, stirring very frequently.  Serve hot over biscuits, grits, etc.